1. Field of the Invention
This invention broadly concerns a control assembly which may be locked along its range of translation. More particularly, it concerns a control assembly using a locking collet whereby locking rotational movement of a rod received within a tubular body serves to lock the control against translation and thereby fix a relative position of a control cable operatively connected to a control actuator.
2. Description of the Prior Art
Various types of control assemblies for actuating remotely located operating mechanisms are well known in the art include various types of levers and the like to which control cables are attached. In some operating environments, it is desirable to use push-pull types of controls for ergometric reasons or to differentiate critical control mechanisms from one another.
In some circumstances, it is desirable to provide push-pull control assemblies which can be held at different positions along their length of travel. Once such example would be in the area of throttle controls wherein a particular engine speed may be selected by the operator. An alternative use for such controls would be to set the position for a snow blower discharge chute. In such instances, it is desirable for the operator to be able to choose among an infinite number of settings within the operating range, rather than being forced to engage the mechanism at one of several preselected positions.
It may be appreciated that once the operator has determined the desired position of the control, such as by obtaining desired engine speed, he may wish to lock that control in position to avoid undesired slippage causing a change in the operating characteristics of the equipment. It may also be appreciated that simplicity of operation and reliability for maintaining the setting so selected, are important characteristics for the design of such a control mechanism.
One design for a control assembly providing locking characteristics is currently known as a "flattened rod". This design consists of a round tube with an oval inner hole and a rod attached to a knob, the rod having a flattened portion, approximately 1" long at the center of the rod. When the rod is rotated, the flattened portion comes in contact with the oval interior surface of the tube, and thereby wedges itself against the reduced dimension along the minor axis of the oval inner surface. This prevents the rod from longitudinal translational movement. One problem with this type of device lies in the necessity of providing close tolerances for the oval interior surface of the tube and the flattened portion across the width of the rod flattened area. If the flattened area ends up slightly wide by a few thousandths of an inch, the control fails to lock. On the other hand, if the flattened area is a few thousandths too narrow, the rod will spin and will not lock against the oval interior surface of the tube. In addition, this design for a control is sensitive to vibration and unlocks very easily. Furthermore, the ratio of rotational torque to longitudinal pull force is approximately 1 to 2 (1 lb. of torque force to 2 lb. of sliding force). Thus, the operator must exert excessive torque to the knob in order to get a fairly high locking force for the rod even when the flattened rod design is constructed according to design specifications.
Another existing design involves the use of a metal collet for locking the control rod in place. This design consists of a tube with a threaded internal section which receives therein a rod over which a threaded metal collet and a slanted collet is positioned. The slanted collet stops against a step on the inside of the tube. The threaded collet is positioned on top of the slanted collet and when the rod is rotated, the threaded collet rotates against the slanted collet, wedging the rod against the slanted collet. This in turn prevents the rod from longitudinal movement. One disadvantage of this metal collet-type of control is that it locks only in the clockwise direction and must be loosened by turning the knob in the counterclockwise direction. Another disadvantage of this type of control is the low torque to longitudinal force ratio, such that once the slanted collet begins to wear, the control begins to slip. Thus, it is not durable and has a relatively short operational life.
Accordingly, there has developed a need for a push-pull type of control assembly of a simplified design not subject to strict tolerances, which provides an acceptable torque to longitudinal force ratio, is durable and provides not only a widely selectable range of positions, but is also reliably lockable along its range of travel.